Various types of air cushion nozzles are known. In one type, the blast air issues from opposed slots, whereas in a second type the blast air issues from holes arranged in rows. Air cushion nozzles with outlet slots have the disadvantage that the suspension properties cannot be exactly predetermined since the width of the opposed slots can differ, for example, due to manufacture or due to the effect of heat during operation. Various outlet cross-sections act so that air issues from the air cushion in the direction of the slot, the blast air from which achieves the least resistance. However, if the direction of discharge cannot be predetermined, the suspension properties of such an air cushion nozzle then cannot be exactly predetermined either. To remove this disadvantage, attempts have been made to arrange spacer elements in the form of rivets distributed longitudinally of the slot. Irrespective of the fact that the width of the slot in the large areas cannot be exactly predetermined, the mounting of spacer elements results in a considerable additional expense in manufacture.
The deficiency of the variation of the cross-section does not arise with rows of holes in place of slots, but other problems are produced. Namely, it is difficult to combine the individual jets to form a jet corresponding to that of a slot nozzle. The joining of individual jets directly after discharge from the holes generally provided in a hole plate causes difficulties. The suspension properties of such a nozzle are, therefore, not an optimum.